Extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems: a review.

http://ntur.lib.ntu.edu.tw/bitstream/246246/90085/1/126.pdf

Aerobic granular sludge: Recent advances

State of the art of biogranulation technology for wastewater treatment.

Extracellular polymeric substances (EPS) were quantified in flocculent and aerobic granular sludge developed in two sequencing batch reactors with the same shear force but different settling times. Several EPS extraction methods were compared to investigate how different methods affect EPS chemical characterization, and fluorescent stains were used to visualize EPS in intact samples and 20-mum cryosections. Reactor 1 (operated with a 10-min settle) enriched predominantly flocculent sludge with a sludge volume index (SVI) of 120 +/- 12 ml g(-1), and reactor 2 (2-min settle time) formed compact aerobic granules with an SVI of 50 +/- 2 ml g(-1). EPS extraction by using a cation-exchange resin showed that proteins were more dominant than polysaccharides in all samples, and the protein content was 50% more in granular EPS than flocculent EPS. NaOH and heat extraction produced a higher protein and polysaccharide content from cell lysis. In situ EPS staining of granules showed that cells and polysaccharides were localized to the outer edge of granules, whereas the center was comprised mostly of proteins. These observations confirm the chemical extraction data and indicate that granule formation and stability are dependent on a noncellular, protein core. The comparison of EPS methods explains how significant cell lysis and contamination by dead biomass leads to different and opposing conclusions.

https://kuscholarworks.ku.edu/bitstream/handle/1808/18929/Sturm_polymeric_substances2005.pdf;sequence=1

Composition and Distribution of Extracellular Polymeric Substances in Aerobic Flocs and Granular Sludge

A critical review of extracellular polymeric substances (EPSs) in membrane bioreactors: Characteristics, roles in membrane fouling and control strategies

The effect of intermittent feeding on aerobic granule structure.

Aerobic granular sludge, without the addition of carrier material, has only been reported in one suspended growth system, the Sequencing Batch Reactor (SBR) operated with short fill and settling periods. Recent studies have demonstrated that extracellular polysaccharides increased with the formation of aerobic granules, and that the shear force may stimulate production of these polysaccharides. In the study described herein, two SBRs were operated with the same shear force (air flow rate 275 L h(-1)) and two different settling times (2 and 10 min). Only the reactor with 2 min settling formed completely granular sludge, although granules were present in both reactors. Community analysis using 16S rRNA PCR products and DGGE showed that the communities diverged quickly after reactor start-up. For samples taken at steady-state, the granular population was more stable and less diverse than the flocculent reactor. EPS extraction of samples using cation exchange resin yielded similar values for aerobic granular sludge and previously reported anaerobic granules. While differences in the protein and TOC content between the flocculent and granular reactors increased appreciably as the sludge became more granular, the protein to polysaccharide ratio was relatively constant. The experiment confirmed previous theories that short settling times in SBRs select for granular sludge. The settling time results in granular sludge having a higher EPS protein content and a less diverse but more stable population.

B.S. McSwain

Papers

Composition and Distribution of Extracellular Polymeric Substances in Aerobic Flocs and Granular Sludge

The effect of intermittent feeding on aerobic granule structure.

Influence of settling time on the formation of aerobic granules

The influence of settling time on the formation of aerobic granules

The SBR and its biofilm application potentials.